Generally, materials may be classified as single crystalline materials, polycrystalline materials, or amorphous materials. A single crystalline material is one that has a single crystalline unit structure, while a polycrystalline material has a structure comprising a plurality of crystalline structure units. An amorphous material may not include a defined crystal structure, as atoms in the amorphous materials may be irregularly bonded to each other. The polycrystalline material typically has many grain boundaries due to the plurality of crystal structure units. The movement of carriers such as electrons or holes may be limited by these grain boundaries.
Thus, in a method of manufacturing a semiconductor device or a system-on-chip (SOC) device including thin-film transistors (TFTs) having stacked structures, single crystalline silicon thin films are often used as channel layers in the active regions of the TFTs. A single crystalline silicon thin film is one that includes a high density of relatively large single crystalline grains in order to improve mobility of these carriers.
To form a single crystalline silicon thin film, an amorphous silicon thin film may be formed on an insulating layer, and the amorphous silicon thin film is thermally treated to form the single crystalline silicon thin film.
Methods of manufacturing a single crystalline silicon thin film are discussed in, for example, Korean Laid-Open Patent Publication No. 2002-91896, Korean Laid-Open Patent Publication No. 2004-98108, Japanese Laid-Open Patent Publication No. 2001-308008, Japanese Laid-Open Patent Publication No. 2002-359159, and U.S. Pat. No. 5,972,105, etc.
In Korean Laid-Open Patent Publication No. 2002-91896, and Japanese Laid-Open Patent Publication No. 2002-359159, a portion of an amorphous silicon thin film is transformed into a single crystalline seed thin film by a first laser heat treatment. Then, a residual portion of the amorphous silicon thin film is transformed into a single crystalline silicon thin film by a second laser heat treatment, using the single crystalline seed thin film formed by the first laser heat treatment as a seed.
A single crystalline silicon thin film, which has a high density of relatively large single crystalline grains, may be easily formed by the above-described method. However, the method may have a disadvantage in that the method may involve the use of a photoresist layer pattern during the first laser heat treatment by which the single crystalline seed thin film is formed, and the method may involve using the laser twice in forming the single crystalline silicon thin film, which may cause a process to become complicated.
The present applicant filed Korean Patent Application No. 2004-43265 on Jun. 12, 2004, which was entitled “Semiconductor Device and Method of Manufacturing the Same” and is now pending in the Korean Intellectual Property Office, regarding a method of forming a single crystalline silicon thin film transformed from an amorphous silicon thin film by irradiating a laser onto the amorphous silicon thin film.
The above method is capable of forming a single crystalline silicon thin film having a high density of relatively large single crystalline grains through a relatively simple process. However, in the method of forming a single crystalline silicon thin film, as shown in FIG. 1, a plurality of seed thin films 10 in a unit cell may be employed. Thus, boundary portions A among multiple single crystalline silicon thin films adjacent to each other exist, so that grain boundaries adjacent to the boundary portions A may be formed. In addition, it may be difficult to form the single crystalline silicon thin film in a peripheral region, in which the seed thin film 10 may not be formed.